Taking into account the growing demands of the automobile industry, new requirements have emerged, which are reflected directly in greater stress on the components of internal combustion engines. So, the present-day engine components, which were not designed for such requirements, undergo early wear. Some of the parts that naturally undergo this effect are the sliding elements, particularly bearings and piston rings.
Numberless developments have been made for the purpose of improving the fatigue strength and wear strength of the components of an internal combustion engine. However, the increase of work pressures on internal combustion engines and the growing friction intensity and contact between the engine components make it difficult to succeed in such attempts, because this lead one of the sliding elements, or the other engine components to wear.
It should also be noted that the future does not hold in store any simplicity for this field of activity; suffice it to observe that more powerful engines are required, which can reach higher and more efficient rotational speed, with lower consumption and high load capacity. All these factors affect the performance of the engine in the long run, impairing the engine operation, or even causing it to fail.
Naturally, in the face of the new requirements, new materials have to be developed, since the known ones are the same that limit the performance of internal combustion engines of today. Some of the most important components to achieve a better performance of an engine are the sliding elements, such as pistons, bearings, etc. Due to the innovations of sliding elements, such as higher hardness, higher fatigue strength and wear strength and, as a result, longer useful life, the automobile industry has kept up with the development of more and more efficient, powerful and durable engines in the face of the high load to which they are subjected.
One understands that the harder the sliding element the less it will wear; but the harder the sliding element the more wear will occur on the softer engine components with which it interacts. Moreover, it is known that the harder the sliding element the more fragile it becomes and the more internal tensions are generated upon manufacture, which leads chiefly to an increase in the probability of there being delamination of the sliding element, detachment of the harder layer that receives the component or even the break, rupture of the component.
In this regard, the prior art has been trying to reach a balance of having a sliding element with sufficiently high hardness, so as not to wear easily in contact with other engine components, but also sufficiently non-aggressive with respect to the other engine components, so as not to cause wear on the other engine components, and sufficiently tough to prevent de-lamination of the sliding element and to prolong the useful life of an engine in general. As can be seen, the equation is far from being easy.
At last, the present invention discloses a sliding element having higher hardness than the prior-art sliding elements, but, on the other hand, it does not cause wear on the other engine components with which the element interacts constantly in operation of the engine.
Finally, one presents a sliding element of high hardness, which undergoes less wear under high load, which does not undergo delamination and also does not cause wear on the other engine components.
Notwithstanding the possible problems identified above, such as wear on other engine components or internal stress in the engine due to the use of a sliding element of high hardness, patent application WO2008098548 and patent DE 10011917 reveal a high demand for sliding elements with higher hardness for use on internal combustion engines.
Patent application WO2008098548 describes a piston ring provided with a sliding layer, which gradually diminishes and is deposited onto at least one face of the piston ring by physical vapor deposition (PVD). However, sliding elements coated by PVD are more susceptible to delamination when compared with sliding elements provided with layers deposited by other processes. So, this technology has serious problems right at the start.
Patent DE 10011917 discloses a piston ring comprising a titanium-nitride coating layer with hardness of about 2200 HV to 2500 HV, by PVD or CVD onto the sliding surface of the piston ring, having a thickness ranging from 5 to 20 microns. The technology disclosed in this document has a serious drawback, which derives from the reduced thickness of the deposited layer, resulting in a reduced useful life of the component, that is, exactly that which one desires to avoid. In the same way, the hardness is excessively high to the point of scratching the cylinder sliding surface.
Thus, it is necessary to achieve a solution that guarantees the requirement of durability, preventing the risk of wear on the components with which the sliding element interacts and also preventing delamination, which naturally tends to increase with the increase in the hardness of the coating layer.